The standard large scale production method for hydrogen peroxide involves the use of anthraquinone as an intermediate. This process is energy-intensive. There has been considerable study over the last 10 to 15 years of alternative processes for direct oxidation of hydrogen by oxygen, but these have not, to our knowledge, been successfully commercialised. There are understandable concerns over the danger of operating with explosive mixtures of hydrogen and oxygen. As examples of recent publications in this field, we mention in particular U.S. Pat. No. 5,135,731, in which gases containing hydrogen and oxygen are reacted in the presence of an aqueous reaction medium, an acid, a promoter, a multifunctional phosphonate and a catalyst, for example Pd and/or Pt which may be on a support such as carbon, alumina, silica, ion exchange resins and other conventional supports. U.S. Pat. No. 4,832,938 is another concept which involves reacting hydrogen with oxygen in an aqueous reaction medium having no, or less than 2%, organic content, a source of protons and chlorine or bromine ions and a combined Pt/Pd catalyst. The catalyst may be supported on carbon, silica or alumina. U.S. Pat. No. 4,009,252 also describes an aqueous medium system using a platinum group metal catalyst.
More recently, Landon et al have published a paper in Phys. Chem. Chem. Phys. 5 (2003) 917 studying a variety of Au and Pd catalysts, and disclosing that a gold alloy catalyst, specifically 5 wt % Au—Pd (1:1 wt %) supported on alumina is an active catalyst for H2O2 formation. Trials were carried out using a reaction medium including supercritical CO2, but overall yields were low because of H2O2 decomposition. Although this academic work is interesting, it seems that high selectivities to H2O2 of 80-90% can be achieved at low temperatures of the order of 1-2° C. but only with low overall yields. Such low temperatures result in an energy-intensive process.
Two other patent documents are U.S. Pat. No. 5,449,655 and EP 0 049 810. U.S. Pat. No. 5,449,655 discloses that activated carbon catalyst supports may be acid-washed to reduce the ash content, and that a further treatment is desirable to improve the catalytic performance for hydrogenation of organic molecules after deposition of a platinum group metal on the supports. The further treatment suitably involves treatment with an oxidising agent such as hydrogen peroxide. This document does not have any relevance to the formation of catalysts for hydrogen peroxide formation by direct reaction of hydrogen and oxygen. EP 0 049 810 is concerned with an improvement in hydrogen peroxide production, using a palladium or palladium-gold catalyst supported catalyst, by selecting catalysts that show decreased hydrogen peroxide decomposition. The improved catalyst is prepared by pretreatment of the catalyst with an aldehyde or a ketone and/or hydrochloric acid.